PVA-containing compositions

ABSTRACT

An extrudable PVA-containing composition is disclosed, which enables PVA articles to be manufactured on conventional extrusion apparatus. The compositions includes a lubricant, such as a fatty acid amide, most preferably octodecanamide and is most preferably formed into pellets by cold pressing. The compositions are suitable for manufacturing a variety of products.

The present invention relates to PVA-containing compositions,particularly filled compositions, to methods of making such compositionsand to methods of extruding PVA-containing compositions.

There is currently a significant and increasing demand forbio-degradable polymers, to replace non bio-degradable polymers whichtake up an ever greater amount of disposal space, such as land-fill, orneed to be incinerated.

Polyvinyl alcohol (PVA) is one bio-degradable polymer which is inwidespread use. As a film, PVA shows a high degree of impermeability toa number of gases. Incorporated into adhesive, PVA shows high adhesivestrength. PVA has significant potential in a wide range of products.However, the applications of PVA have been limited because there iscurrently no formulation of PVA or PVA-containing composition which canreadily be extruded.

While attempts have been made to extrude articles from PVA, it has beenfound that melt extruded PVA becomes very unstable and significantresidues become adhered to the surfaces of the extrusion apparatus,requiring very careful control of process conditions, specialisedextrusion apparatus and frequent shut down of the extrusion process andpurging of the apparatus.

It is known to polymerize ethylene with vinyl alcohol to provide acopolymer of ethylene-vinyl alcohol, in an attempt to retain thedesirable properties of PVA whilst simultaneously obtaining anextrudable polymer. One such copolymer is marketed under the trade markSOARNOL (registered trade mark of the Nippon Synthetic Chemical IndustryCo, Limited). However, it is found that this copolymer has effectivelylost all of the advantageous properties of PVA and is not an effectivealternative to an extrudable PVA.

A chemically modified PVA is also known and sold as VINEX (registeredtrade mark of Air Products). This suffers, however, from the fact thatsome of the advantageous PVA properties are adversely affected by thechemical modification.

The search for biodegradable polymers is acute in relation to certainsanitary products such as diapers and sanitary towels. However, theseproducts typically comprise superabsorbent materials and at present suchmaterials are only available in combination with conventional nonbio-degradable polymers.

The present invention is concerned, at least in preferred embodiments,with providing PVA-containing compositions, methods of manufacturing thesame and methods of extruding PVA-containing compositions which overcomeor at least ameliorate some of the disadvantages identified in the art.

Accordingly, a first aspect of the invention provides a PVA-containingcomposition comprising a blend of PVA and an amount of lubricanteffective to render the blend extrudable.

The lubricant preferably comprises a fatty acid amide and thecomposition may advantageously further comprise a plasticiser, theresultant blend being suitable for extrusion in conventionalmelt-extrusion apparatus. In embodiments of the invention, aPVA-containing composition comprises up to 20%, especially 5 to 15%,plasticizer and up to 5%, especially 0.5 to 2.5%, lubricant, by weight.

The composition of the present invention is thus an extrudablePVA-containing polymer, typically with a flexural modulus similar toother extrudable polymers. Known advantageous properties of PVA, such asits high tensile strength, good puncture resistance, and good barriercharacteristics are retained in an extrudable composition which can beprocessed on current extrusion lines, blow-moulders and injectionmoulders without modification, and without the processing problems suchas thermal degradation and high temperature cross linking, observed inattempts to extrude articles using hitherto known PVA-containingcompositions.

In embodiments of the invention, extrudable PVA-containing compositionshave been obtained comprising fully hydrolysed PVA as well as partiallyhydrolysed PVA, and including PVA that is 70% or more hydrolysed.

Further embodiments of the invention provide PVA-containing compositionsin which the molecular weight of the PVA varies from around 20,000, insome cases from around 10,000, to greater than 150,000. Generally, theapplication of the present invention is not limited to PVA of anyparticular percent hydrolysis nor of any particular molecular weight.

A second aspect of the invention provides a filled PVA-containingcomposition comprising a blend of PVA plus filler. In this composition,the filler is effectively a bulking agent and is relatively inexpensivecompared to the PVA, thus a composition is obtained retainingadvantageous properties of PVA whilst being cheaper per unit weight toproduce.

In both aspects, the invention preferably provides a PVA-containingcomposition in the form of pellets or tablets. These preferably have asize of between about 1 mm and 5 mm in diameter and are suitablyobtained by a method of the invention in which PVA, preferablysubstantially uncompounded and in powder or granular form, is mixed withat least one of lubricant and filler, and optionally other compoundingingredients, and cold pressed to form a tablet or pellet. Thiscold-pressing method is substantially as described in WO-A-98/26911 inrelation to different polymers.

With this method, the ingredients can be uniformly mixed and compoundedin the correct proportions for the final product, and made into a formthat is easier to handle than powder. In addition, since the mixture iscold pressed rather than melted, problems of thermal degradation orvariation in properties are reduced.

References to “cold pressing” are intended to imply applying pressure tothe powder to cause agglomeration without substantial melting of thepolymer. The temperature is preferably less than about 100 degreesCelsius, more preferably less than about 70–80 degrees Celsius.Preferably heat is not applied directly to the mixture. However, heatmay be generated by mixing and/or pressing, and this may be allowed towarm the mixture, or cooling may be provided. It is permissible for someheat to be applied directly if necessary to facilitate binding. Somemelting of the polymer or other ingredients may occur, particularly on amicroscopic scale as a result of pressure at the interface betweenadjacent particles, but it is important that the bulk of the polymergranules do not liquefy.

Preferably, the mixture is compressed in discrete quantities intotablets or pellets, for example in a tablet press; this may provide morereliable agglomeration.

However, it is possible for the mixture to be extruded under pressurethrough an orifice, the pellets forming following exit of the mixturefrom the orifice. In such a case, binder or moisture may be added to themixture, preferably as the mixture is extruded, or after preliminarymixing of the constituents.

Preferably, the mixture is substantially dry, but includes sufficientresidual moisture to bind the tablets or pellets on pressing. Thisavoids the need to add a separate binder, and allows the tablets orpellets to be broken more easily as they enter the extruder simply bydrying them further. When water is relied upon for binding, it isdesirable to ensure that the tablets or pellets are dried prior toextruding, for example at between 40 and 80 degrees Celsius for 4–8hours; this alleviates problems of vapour formation during extrusion.The moisture content is desirable to form the tablets, but afterforming, the tablets should in most cases retain their shape even whendried.

Preferably, the moisture content is less than about 10% by weight, andpreferably greater than 0.01% by weight, more preferably less than about5%. If the pellets or tablets are extruded or otherwise formed atrelatively low pressures, however, the moisture content may be about 20%or even higher to ensure binding. If the pellets are too moist, they maytend to stick together, inhibiting flow, and drying after forming may bedesirable.

The moisture may comprise residual moisture in the polymer or in one ormore of the compounding ingredients. In this way, moisture can beprovided automatically simply by not drying the ingredients fully priorto mixing.

It is preferred that the filled PVA-containing composition isextrudable, and hence preferred that the filled PVA-containingcomposition further comprises an effective amount of a lubricant torender the composition extrudable. The lubricant suitably comprises afatty acid amide or a plasticiser or a mixture of both a fatty acidamide and a plasticiser.

The lubricant in compositions of the invention is provided so as toimprove the thermal stability of the composition under extrusion. Thelubricant may be referred to as an internal lubricant, in that itsfunction is to improve lubrication between the polymer chains.Compositions of the invention may be intended for use in or inconnection with food stuffs, and hence it is preferred that thelubricant is approved for food use. It is further preferred that thelubricant is a fatty acid amide, and particularly a straight or branchedC₁₂–C₂₄ fatty acid amide, more particularly C₁₆–C₂₀. Particularly andsurprisingly good results are obtained if the lubricant comprisesstearamide, a straight chain C₁₈ fatty acid amide.

The compositions of the invention typically further include aplasticiser, to lower the melt temperature of the polymer underextrusion. The plasticiser may suitably be selected from glycerine,ethylene glycol, triethylene glycol, low molecular weight polyethyleneglycols and low molecular weight amides. A particularly preferredplasticiser comprises or consists of glycerol.

While the proportion of components present may vary in compositions ofthe invention, embodiments of the invention generally comprise, byweight, up to 50% filler and up to 5% lubricant. More particularembodiments of the invention comprise, by weight, 5–50% filler, 40–80%PVA, up to 5% lubricant and 5–20% plasticizer.

Compositions of the invention are thus extrudable, but it may be thatease of extrusion depends partly upon the state of the extrusionapparatus, in particular the roughness of surfaces in the apparatus. Infurther embodiments of the invention, the compositions comprises anadditional lubricant, which may be referred to as an external lubricant,to prevent or reduce adhesion of the composition to such surfaces. Thisexternal lubricant is typically present at 0.001 to 0.1% by weight ofthe composition and preferably approved for food use, in the same way asthe internal lubricant. Stearate salts are suitable external lubricants,in particular magnesium, lead or zinc stearates.

Fillers for incorporation into compositions of the invention maysuitably be selected from conventional polymer fillers. Typically thefiller is an inert, inorganic material and a particularly preferredfiller is or comprises talc, calcium carbonate. In a specific embodimentof the invention, this talc may be micronised, such as in particles witha mean size of about 20 microns and may further be coated, such as witha stearate. One such coated, micronised talc is available from Croxtonand Gary as 90T (trade mark of Croxton and Gary).

It is further an option for the filler to comprise or consist of asuperabsorbent material. In a specific embodiment of the invention,described in an example below, a filled PVA-containing compositioncomprises a superabsorbent which contains cross-linked sodiumpolyacrylate (available from Alloid Colloids as SALISORB CL31(registered trade mark)). Filled compositions of the invention maynevertheless contain superabsorbent material of substantially any type.Incorporation of such superabsorbent material confers the particularadvantage that sanitary products such as diapers and sanitary towels,hitherto major components of waste storage sites such as land-fillsites, may now be made of or comprise a significant proportion ofbio-degradable material.

A number of water-absorbent compositions are known and suitable for useas the filler in embodiments of the invention. For example, U.S. Pat.Nos. 3,954,721 and 3,983,095 disclose preparations for derivatives ofcopolymers of maleic anhydride with at least one vinyl monomer infibrous form. The fibrous copolymers are rendered hydrophilic andwater-swellable by reaction with ammonia or an alkali metal hydroxide.U.S. Pat. No. 3,810,468 discloses lightly cross-linked olefin-maleicanhydride copolymers prepared as substantially linear copolymers andthen reacted with a diol or a diamine to introduce cross-linking. Theresultant lightly cross-linked copolymers are treated with ammonia or anaqueous or alcohol solution of an alkali metal hydroxide. U.S. Pat. No.3,980,663 describes water-swellable absorbent articles made fromcarboxylic polyelectrolytes via cross-linking with glycerine diglycidylether. These patents are incorporated herein by reference.

European Published Application No. 0 268 498 (incorporated herein byreference) describes a water-absorbent composition formed by causing asubstantially linear polymer of water-soluble ethylenically unsaturatedmonomer blends comprising carboxylic and hydroxylic monomers tocross-link internally.

Further examples of water-absorbent compositions are those produced froma copolymer of an α,β unsaturated monomer having at least one pendantunit selected from a carboxylic acid group and derivatives thereof and acopolymerisable monomer. A proportion of the pendant units are presentin the final copolymer as the free acid and a proportion as the salt ofthe acid. These copolymers are capable of being cross-linked, eitherinternally or with a variety of cross-linking agents, to form thewater-swellable composition. Examples of water-swellable compositions ofthis type can be found in U.S. Pat. Nos. 4,616,063, 4,705,773,4,731,067, 4,743,244, 4,788,237, 4,813,945, 4,880,868 and 4,892533 andEuropean Patent Nos 0 272 074 and 0 264 208 and European PublishedApplication No. 0 436 514 which are incorporated herein by reference.

Derivatives of carboxylic acid groups include carboxylic acid saltgroups, carboxylic acid amide groups, carboxylic acid imide groups,carboxylic acid anhydride groups and carboxylic acid ester groups.

Other examples of water-absorbent compositions can be found in U.S. Pat.No. 4,798,861, WO93/17066, WO93/255735, WO 93/24684, WO93/12275,European Published Application Nos 0 401 044, 0 269 393, 0 326 382, 0227 305, 0 101 253, 0 213 799, 0 232 121, 0 342 919, 0 233 014, 0 268498 and 0 397 410, British Patent Application Nos 2 082 614, 2 022 505,2 270 030, 2 269 602 and 2 126 591, U.S. Pat. Nos. 4,418,163, 4,418,163,3,989,586, 4,332,917, 4,338,417, 4,420,588 and 4,155,957 and FrenchPatent Application No. 2 525 121 which are all incorporated herein byreference.

The extrudable compositions of the invention are suitable formanufacture of substantially any article made using currently extrudablepolymers, including films and bottles and any other articles. Thecompositions are suited to manufacture of filaments and fibre, for usein spunbond, non-woven and melt-blown applications. The composition issuitable also for manufacture of such articles as agri-chem sachets,mulch films, plant pots, domestic bags, diapers, drinking straws, femcare products, hangers, incontinence pads, sachets, six pack rings,disposable clothing, expanded foams, gloves, film canisters, golf tees,shot gun cartridges, bed pans, bottles, bowls, cotton buds, hospitalcurtains, “one-use” sterile products and packaging materials.

Compositions of PVA have good gas and fossil fuel barrier properties andare particularly suitable for making balloons and disposable packagingfor oil and the like.

Good results have been obtained with embodiments having the followingmake up, by weight:

-   (a) 40 to 80% PVA;-   (b) 5 to 50% filler;-   (c) 5 to 15% plasticiser, preferably glycerol;-   (d) 0.5 to 2.5% lubricant, preferably a fatty acid amide as an    internal lubricant, most preferably octodecanamide.

Particularly good results have been obtained in embodiments of theinvention having the following make-up, by weight:

-   (a) 40 to 70% PVA;-   (b) 20 to 50% filler, preferably a micronised inorganic material    such as talc, preferably coated with stearate;-   (c) 8 to 15% plasticizer, preferably glycerol;-   (d) 0.5 to 1.5% internal lubricant, preferably a fatty acid amide,    most preferably octodecanamide; and-   (e) 0.0001 to 0.1% external lubricant, preferably stearate.

The composition may contain residual moisture, sufficient to enable thecomposition to be bound as a cold-pressed tablet.

Further advantageous results have been obtained in compositions of theinvention comprising, by weight:

-   -   50 to 60% PVA;    -   30 to 40% stearate-coated calcium carbonate;    -   8 to 15% glycerol;    -   0.5 to 1.5% octadecanamide; and    -   0.0001 to 0.1% zinc stearate.

In a third aspect, the invention provides a method of making anextrudable PVA-containing composition comprising blending PVA with alubricant, said lubricant including a fatty acid amide. The methodpreferably comprises blending PVA with a fatty acid amide in thepresence of an amount of moisture sufficient to bind the compositioninto tablets or pellets upon cold pressing.

The amount of lubricant blended with the PVA is typically restricted bythe fact that, above a certain percent, excess lubricant separates outfrom the blend, and generally lubricant is blended at up to 5% by weightof the PVA present. The method thus conveniently enables tablets orpellets of the composition to be prepared as the feedstock for anextrusion. Blending of the components of the composition is achievedusing conventional apparatus, one such example being a high speedblender.

The method may optionally comprise adding small amounts of moisture tothe components to be blended, such as by dripping water into the blend.Preferably, PVA and lubricant are fed into a high speed mixergravimetrically.

In a fourth aspect, the invention provides a method of making aPVA-containing composition comprising blending PVA and a filler, whereinthe filler comprises a superabsorbent material. It is preferred thatblending is carried out in the presence of sufficient moisture to bindthe composition into tablets or pellets upon cold pressing, the moistureoptionally being present in the starting materials of the blend or beingintroduced into the blend, such as by drip-feeding.

A fifth aspect of the invention provides a method of extruding aPVA-containing composition so as to form an extruded product whichcontains PVA, comprising:

-   -   blending PVA with at least one component selected from a        lubricant and a filler; and    -   cold pressing the resultant blend into pellets or tablets;    -   wherein the pellets or tablets comprise the polymer feedstock        for extrusion of an extruded product containing PVA.

The PVA is preferably blended with one or more lubricant or fillercomponents in the presence of sufficient moisture to bind the blend uponcold pressing. An advantage of the method is that the PVA-containingfeedstock for the extrusion step is obtainable substantially withoutmelting of the PVA. This improves the stability of the PVA duringsubsequent extrusion. Hitherto, as has been recognised in the presentinvention, attempts to extrude a PVA-containing feedstock largely failedas the PVA already had a heat history, ie had been wholly or partiallymelted in processing stages prior to the extrusion stage. The presentinvention avoids the disadvantage of introducing such a heat historyinto the PVA-containing composition.

A sixth aspect of the invention provides a method of extruding aPVA-containing composition comprising blending PVA and at least oneoptional component selected from a lubricant and a filler to form afeedstock for an extrusion process, the feedstock being in the formsuitably of powder, pellets or tablets, and extruding the feedstock intoa product, wherein the feedstock is prepared substantially withoutmelting of the PVA.

A seventh aspect of the invention provides a method of extruding apolymer composition containing a heat sensitive polymer, comprisingblending the heat sensitive polymer with one or more optional componentsselected from a filler and a lubricant to form a feedstock for anextrusion process, the feedstock being suitably in the form of powder orpellets or tablets, and extruding the feedstock into an extrudedproduct, wherein the feedstock is prepared substantially without meltingof the heat sensitive polymer.

Optional and preferred features of the first and second aspects of theinvention are, similarly, optional and preferred features of the thirdto seventh aspects of the invention.

The invention is now described in the following non-limiting examples.

EXAMPLE 1

A blend of, by weight, approximately 60% fully hydrolysed PVA, 30%calcium carbonate, 10% glycerol, 0.01% zinc stearate and 1%octadecanamide was prepared in a high speed blender. It was found tohave a white/cream colour with the following properties:

density 1.65 g/cm³ melt density 1.46 g/cm³ at 200° C. (under ISO 1183)MFR 357 (10 mins/200° C./21.6 kilograms, under ISO 1133) melttemperature 200° C. processing temperature 190–200° C. residence time upto 15 minutes drying time 4 hours at 80° C.

EXAMPLE 2

A blend was prepared in a similar way to example 1 of, by weight,approximately 60% partially hydrolysed PVA, 30% calcium carbonate, 10%glycerol, 0.01% zinc stearate and 1% octadecanamide. This was found tohave the following properties:

density 1.65 g/cm³ melt density 1.38–1.40 g/cm³ at 190° C. (under ISO1183) MFR 22 (10 mins/190° C./5 kilograms, under ISO 1133) apparent meltviscosity 236/49 (Pa · s 1,000 s/10,000 s) melt temperature 200° C.processing temperature 190–200° C. residence time up to 15 minutesdrying time 4 hours at 80° C.

EXAMPLE 3

The PVA-containing compositions of examples 1 and 2 were examined fortheir extrudability in injection-moulding machines made by Brabender,Killion, Windsor, Hesas, Battenfield, Fischer, Demag and Arburg.Extrusion processing was carried out using a single full flight screwwith constant pitch. The barrel temperature had a profile of 180–200° C.(melt 190–210° C.) and the screw speed varied typically between 20 and120 rpm. Shut down of the apparatus was carried out by maintaining thetemperature for up to 15 minutes with screw rotation stopped, over aperiod of 3 hours reducing the temperature to 100° C. with screwrotation stopped and subsequently completing the shut down by turningthe machine off.

Whether or not a given composition is extrudable (by which is meant oncommonplace extrusion apparatus) will normally be clear to one skilledin the art. In the event that a test is required, however, it issuggested that extrudability is determined by attempting extrusion onone or more of the above-named manufacturers machines using a singlefull flight screw with constant pitch with speeds and temperatures inthe above range. If the composition extrudes reliably on at least two ofthe above machines with routine adjustment of parameters, it is to bedeemed extrudable; if consistent problems are obtained and extrusion isonly possible under highly specific conditions or on specialisedequipment, it is to be deemed not to be extrudable.

The compositions of both examples 1 and 2 were satisfactorily extrudedinto a range of films and tubes blow-moulded containers of various sizesand colours and injected moulded products.

EXAMPLES 4–9

PVA-containing compositions were prepared as blends of the followingcomponents in the amounts shown:

EXAMPLE Components 4 5 6 7 8 9 PVA - fully hydrolysed — — — 50 60 55PVA - partially 50 60 55 — — — hydrolysed Calcium carbonate 40 30 30 4030 30 (coated) Glycerol 9 9 14 9 9 14 Octadecanamide 1 1 1 1 1 1 ZincStearate 0.01 0.01 0.01 0.01 0.01 0.01

EXAMPLE 10

A further filled PVA-containing compositions was prepared as a blend of,by weight, approximately 60% partially hydrolysed PVA, 30% cross-linkedsodium polyacrylate (a superabsorbent), 9% glycerol, 1% octadecanamideand 0.01% zinc stearate.

As far as extrusion apparatus is concerned, it is advantageous to usechrome plated screws and for the melt flow path to use chrome platedsurfaces and gradual tapers to streamline the melt.

The invention thus provides PVA-containing compositions for use in themanufacture of biodegradable articles. The invention extends tocombinations of all features individually disclosed. In particular,optional or preferred features of any of the apparatus, product ormethod aspects may be combined with features of other aspects.

1. A polymer feedstock in the form of a cold-pressed tablet or pelletfor use in extrusion of an extruded product containing PVA, thecold-pressed tablet or pellet comprising, by weight of the feedstock, ablend of: 40 to 70% PVA; 8 to 15% plasticizer; 0.5 to 1.5% internallubricant; 0.0001 to 0.1% external lubricant; and 5 to 50% solidparticulate filler.
 2. A polymer feedstock according to claim 1 whereinthe internal lubricant comprises a fatty acid amide.
 3. A polymerfeedstock according to claim 2 wherein the fatty acid amide is astraight or branched C12–C24 fatty acid amide.
 4. A polymer feedstockaccording to claim 1 wherein the plasticiser is selected from the groupconsisting of ethylene glycol, glycerol, triethylene glycol,polyethylene glycols and C2–C8 amides.
 5. A polymer feedstock accordingto claim 1 wherein the filler comprises inert, inorganic material.
 6. Apolymer feedstock according to claim 1 wherein the filler comprises asuperabsorbent material.
 7. A polymer feedstock according to claim 1wherein the filler comprises both an inert, inorganic material andsuperabsorbent material.
 8. A polymer feedstock according to claim 5wherein the inorganic filler comprises calcium carbonate.
 9. A polymerfeedstock according to claim 1 wherein the external lubricant comprisesa stearate.
 10. A PVA-containing polymer feedstock in the form of acold-pressed tablet or pellet comprising, by weight of the feedstock: 40to 80% PVA; 5 to 50% solid particulate filler; 5 to 15% plasticizer; and0.5 to 2.5% internal lubricant.
 11. A polymer feedstock according toclaim 10, comprising, by weight of the feedstock: 40 to 70% PVA; 20 to50% solid particulate filler; 8 to 15% plasticizer; 0.5 to 1.5% internallubricant; and 0.0001 to 0.1% external lubricant.
 12. A polymerfeedstock according to claim 10 wherein a fatty acid amide is providedas internal lubricant.
 13. A polymer feedstock according to claim 11wherein stearate is provided as external lubricant.
 14. A polymerfeedstock according to claim 11 comprising, by weight of the feedstock:50 to 60% PVA; 30 to 40% stearate-coated calcium carbonate; 8 to 15%glycerol; 0.5 to 1.5% octadecanamide; and 0.0001 to 0.1% zinc stearate.15. A polymer feedstock according to claim 1 prepared without liquefyingthe bulk of the polymer granules.
 16. A polymer feedstock according toclaim 1 having a moisture content less than about 10% by weight of thefeedstock but greater than 0.01% to bind the pellets or tablets.
 17. Amethod of making a PVA-containing polymer feedstock according to claim 1comprising blending the PVA with the plasticizer, the internallubricant, the external lubricant and the filler, said internallubricant including a fatty acid amide, in the presence of an amount ofmoisture sufficient to bind the polymer feedstock into tablets orpellets upon cold pressing and cold pressing the feedstock into tabletsor pellets.
 18. A method according to claim 17 comprising blending, in ahigh speed blender, the PVA and the internal lubricant.
 19. A methodaccording to claim 17 comprising adding moisture to the components to beblended.
 20. A method according to claim 17 wherein PVA and lubricantare fed into a high speed mixer gravimetrically.
 21. A method of makinga PVA-containing polymer feedstock according to claim 17, wherein thefiller comprises a superabsorbent material.
 22. A method of extruding aPVA-containing polymer feedstock comprising forming a feedstockaccording to claim 1 and extruding the feedstock into a product, whereinthe feedstock is prepared.